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题型:解答题 题类:常考题 难易度:普通
等差关系的确定+++++++++
(Ⅰ)求证: 是等差数列;
(Ⅱ)当x1= 时,求x100 .
①若数列{an}既是等差数列又是等比数列,则Sn=na1;
②若Sn=2n﹣1 , 则数列{an}是等比数列;
③若Sn=an2+bn(a,b∈R),则数列{an}是等差数列;
④若Sn=an(a∈R),则数列{an}既是等差数列又是等比数列.
其中正确结论的序号是{#blank#}1{#/blank#}.
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